help tweaks

lib/cmd/install.ps1

@@ -5,6 +5,9 @@ param($app)
 
 . "$(split-path $myinvocation.mycommand.path)\..\core.ps1"
 . (resolve ../manifest.ps1)
+. (resolve ../help_comments.ps1)
+
+if(!$app) { "ERROR: <app> missing"; my_usage; exit }
 
 $manifest = manifest $app
 if(!$manifest) { abort "couldn't find manifest for '$app'" }

lib/help_comments.ps1

@@ -11,6 +11,6 @@ function help($text) {
 	$help_lines -replace '(?ms)^# (Help: )?', ''
 }
 
-function my_usage {
-	"usage: $(usage (gc $myInvocation.PSCommandPath -raw))"
+function my_usage { # gets usage for the calling script
+    usage (gc $myInvocation.PSCommandPath -raw)
 }